Wash the car. Wash the windows. Wash the floor. What are you doing to that poor sponge anyway? Poor sponge? That washing aid you’re using, if your lucky enough to have a true sponge, is all thats left of a marine animal.

Sponges are strange creatures and not at all like most of the animals with which we are familiar. They can be almost any color, from white to gray to any shade of red or yellow to purple and black. They have no head, body, arms, legs or any other obvious structures that we generally associate with animals. Some sponges live singly. Others live in crowded colonies that form crust like layers over rock surfaces. Individual sponges can be as small as a centimeter or as large as two meters across. Our washing sponge certainly doesn’t look alive. In fact, it isn’t. The “sponge” that most of us think about when we hear the word is really only the skeleton of a sponge animal. The skeleton of a living sponge would be surrounded with cells. the body plan of a sponge is simple. Sponges are considered to have the lowest multicellular organization of all animals. This distinction elevates sponges to just one step above the one celled protozoans.

When examining a living sponge, a close look reveals that the sponge is covered with many small holes or incurrent pores . The pores explain the name of the phylum to which sponges belong, Porifera , which means “pore bearing”. We also see a larger opening called the osculum (Latin for “little mouth”). If we were to place a drop of food coloring near the sponge, we would be able to follow the dye as it moved into the incurrent pores and out the osculum.

The colored water is moved through the sponge by the movement of whip-like structures (flagella) found on the cells that line the inside of the sponge’s body. These cells are shaped somewhat like a goblet and are called collar cells or choanocytes. The current caused by these collar cells moves not only water but also plankton and other small bits of organic matter the sponges use for food. The current also helps supply oxygen to the living cells. Through water movement, the sponge draws its food and oxygen to itself. Moving the environment through the sponge keeps the sponge from having to move through the environment. The adult sponge, therefore, can and does spend its life permanently attached by its base to a rock or shell or some similar substrate. The sponge is sessile, or relatively non-moving. (Q1 & 2).

A simple sponge has a hollow body, and the body wall is formed of two layers of cells separated by a layer of jelly-like material. The outer layer or epidermis protects the sponge. The inner layer contains the collar cells. The jelly layer is a mixture of loose cells, spicules and/or spongin. The spicules are noncellular skeletal structures that help support the sponge’s body. Spongin is a tough, fibrous protein material that also helps to support the sponge. (Q3)

Spicules are secreted by living cells. They are small rods composed of either lime (calcium carbonate) or glass (silica). The spicules come in a variety of shapes and sizes. Each species of sponge has its own special combination of spicules. Like a fingerprint, these combinations may be used to identify the species of sponge.

Biologists have divided spicules into four basic shapes:

1. single axis or straight spicule (monoaxon)

2. three pronged or multiple of three spicule (triaxon)

3. four pronged spicule (tetraxon)

4. many pronged spicule (polyaxon) (Q4)

Spicules are secreted in many sponges by small amoeba-like cells called amoebocytes . These amoebocytes also distribute digested food and oxygen to other cells as they wander through the jelly-like layer. Often sponges produce two types of spicules. The large spicules are called megascleres and the smaller spicules of a different design are called microscleres.